The Phases of Locusts in South Africa

Abstract

Adding together all the hoppers listed above, we find that 637 individuals were reared in these experiments from 34 different pairs of adults; 394 were reared in complete isolation, and 243 under crowded conditions, but each crowd consisted of the progeny of one pair only. The majority of those isolated were placed in isolation on the day of hatching, but some first lived in a crowd for a week or two before being used to replace isolated individuals that had died.Comparing the results in Tables XXI and XXII, we noted that the isolated hoppers acquired thesolitariacharacters, while those crowded tended to develop thegregariacharacters, regardless of whether the parents had beengregariaorsolitaria. Only two isolated hoppers from the pair L.p.352 showedgregariacharacters, and one of these had lived in a crowd and had acquiredgregariacharacters before it was placed in isolation in its second instar. Table XXIII shows that crosses betweengregariaandsolitariagave the same results.In the second generation (Table XXIV) the progeny of the P1gregariapair 352 reacted to isolation and crowding in the same way as all other hoppers, and the same was true of the F2back-cross togregaria(L.p.569).Examining the hypothesis of Potgieter in the light of these experiments, we find that the data presented in Tables XXI to XXIV are in direct contradiction with the three phases enumerated above. Instead of giving a majority ofgregaria, the matings ofgregariabygregariaproduced bothgregariaandsolitariaaccording to the conditions under which the progeny were reared. According to the second thesis, the crossing ofsolitariaandgregariashould always result in a majority ofgregaria, but Table XXIII shows that 90 isolated hoppers all becamesolitaria. Thirdly, the mating ofsolitariawithsolitariais supposed never to producegregariaprogeny; Table XXII shows that the progeny of these crosses developedgregariacharacters when crowded andsolitariawhen isolated.